Modern vehicles are increasingly using an auto stop feature in which the vehicle engine is shut down to conserve fuel when the vehicle stops. During auto stop, vacuum pressure may not be available for operation of the vehicle brake system. If the vacuum level is low or becomes low while the engine is off, an expensive electric vacuum pump or engine startup may be necessary to achieve an adequate level of vacuum pressure for braking.
Accordingly, a hydraulic brake assist vacuum maintenance system and method which maintains hydraulic pressure for braking using Hydraulic Brake Assist (HBA) during auto stop engine shutdown is needed.